The combination of complete RBBB and abnormal left axis deviation (bifascicular block) is a significant conduction abnormality that indicates partial bilateral bundle-branch block and a risk for complete heart block.
The pattern of complete right bundle-branch block (RBBB) combined with abnormal left axis deviation is shown to be the predominant conduction abnormality during orthograde (antegrade) conduction in patients who have experienced transient or permanent complete heart block (59% of a series of 44 patients). Sequential records on the same patient are presented showing progressive development of the complete pattern from left parietal and peri-infarction block alone and also from RBBB with normal axis deviation. Underlying abnormality is a partial bilateral bundle-branch block, that is, complete RBBB and involvement of the anterior-superior subdivision of the left bundle. The incidence of this pattern in 5,500 consecutive hospital records was 1%. Of these, 10% manifested complete heart block. It is suggested that a history of syncope or dizziness in a patient with the above pattern may denote that episodes of transient heart block have occurred.
Lasser et al. (1968) studied this question.